Field of the Invention
Present invention relates to a silicon single crystal manufacturing apparatus and a silicon single crystal manufacturing method. A high quality silicon single crystal having an intended crystal characteristics can be obtained by the apparatus and method. In the apparatus and the method, the melt level position of the silicon melt is adequately regulated when the silicon single crystal is pulled from the silicon melt by Czockralski method.
Description of Related Art
Conventionally, varieties of methods for manufacturing the silicon single crystal are known. However, the most representative method for manufacturing the silicon single crystal is the Czockralski method (hereinafter, referred as CZ method). In the growing silicon single crystal in the CZ method, the silicon melt is formed by melting poly-silicon in a crucible. Then, a seed crystal is immersed in the silicon melt. By pulling the seed crystal in the predetermined rotation speed and pulling speed, the silicon single crystal having an cylindrical shape is grown below the seed crystal.
When the silicon single crystal is grown by the CZ method, distribution and types of defects included in the single crystal depend on ratio of the pulling speed V of the silicon single crystal and the temperature gradient G in the silicon single crystal in the growing direction (herein after referred as V/G).
If the V/G value is too high, excessive voids are formed and the micro-voids (the defect referred “COP” generally), which are aggregates of the voids, are formed. If the V/G value is too low, excessive amount of the interstitial silicon atoms are formed, and the translocation clusters, which are aggregates of the interstitial silicon atoms, are formed. Therefore, in order to manufacture a silicon single crystal free of the COP and the translocation cluster, the V/G value has to be controlled to put the V/G value in an appropriate range in the longitudinal and the radial direction of the silicon ingot.
In the radial direction of the single crystal, the V value is constant at any location. Therefore, it is necessary to design the hot-zone in the CZ reactor in such a way that the temperature gradient G is set to be in a predetermined range in the radial direction of the single crystal. Next, in terms of the longitudinal direction, the G value varies depending on the pulling length of the single crystal. Thus, in order to keep the V/G value in a predetermined range, the V value has to be varied in the longitudinal direction of the single crystal.
Today, crystals free of the COP and the translocation cluster are mass-produced by controlling the V/G value even if the silicon single crystals have diameter of 300 mm.
However, the silicon wafers free of the COP and the translocation clusters pulled by controlling the V/G value are not consist within the entire surfaces, and include regions that respond differently in the thermal treatment. For example, there are three regions between the COP-forming region and the translocation cluster-forming region. The three regions are OSF region, Pv region, and Pi region in the order of the larger V/G values.
The OSF region contains the plate-shaped oxygen precipitates (OSF nucleus) in the as-grown status, which is the status that no thermal treatment is performed after the single crystal growth. When the OSF region is heat-oxidized at a high temperature (generally 1000° C. to 1200° C.), the OSF (Oxidation Induced Stacking Fault) is formed. The Pv region includes the oxygen precipitation nucleus in the as-grown status. When the Pv region is subjected to a two-step thermal treatment with a low temperature and a high temperature (800° C. and 1000° C., for example), the oxide precipitate can be easily formed in this Pv region. The Pi region does not include the oxygen precipitate nucleus in the as-grown status. In the Pi region, formation of the oxygen precipitate is rare after thermal treatment.
There is a demand for a high quality silicon single crystal with separated Pv and Pi regions (hereinafter referred as PvPi crystal). In order to grow the PvPi crystal, accurate controlling of the V/G value is needed.
Generally, the V/G value is controlled by regulating the pulling speed V. In this V/G value control, the G value in the pulling of the silicon single crystal is largely affected by the distance (interval) between the melt level of the silicon melt and the heat shield provided to face the melt level. The furnace body is dismantled to clean in every pulling batch in the silicon single crystal pulling, and the furnace is re-assembled for the next batch. Therefore, the distances between the melt level of the melt and the heat shield are varied in each pulling batch.
Conventionally, the distance between the melt level of the melt and the heat shield is set by an operator based on visual observation in every pulling batch, making the distance varies in every pulling batch. Therefore, in order to manufacture a silicon single crystal with an intended defect region by controlling the V/G value, it is necessary to measure the melt level position of the silicon melt accurately during the silicon single crystal pulling and to regulate the amount of vertical movement of the crucible precisely.
For example, Patent Literature (PTL) 1 (JP1676655B) discloses a method to measure the melt level position of the silicon melt accurately. In the method disclosed in PTL 1, a fire resistance rod, made of quartz for example, is provided to the heat shield covering the melt level of the melt at the end part of the heat shield facing the melt level of the melt. Then, the standard melt level position (hereinafter referred as melt level) is defined as the melt level position that the fire resistance rod touches the melt level of the melt.
Also, a method, in which the contacting of the seed rod to the melt level of the melt is detected first and used the contacting position as the standard melt level position, is disclosed in PTL 2 (JP2132013B).